The present invention relates to video-signal output apparatuses and video-signal input apparatuses, and in particular, to a video-signal output apparatus having a function of scrambling a video signal and outputting the signal, and a video-signal input apparatus having a function of descrambling an input scrambled video signal.
In recent years, various types of so-called “high definition (HD)” systems have become known in which image quality is enhanced by using a greater number of scanning lines than that used in a conventional television system or employing a noninterlaced (progressive scanning) method. The various types of HD systems include, for example, a system called “720P (progressive)” that uses 720 scanning lines to perform progressive scanning, a system called “1080I (interlaced)”, and other proposed systems. A conventional television system such as the NTSC system (“525I”) is called a “standard definition (SD)” system.
A picture displayed by the HD system has an image quality higher than that displayed by the SD system, even if the picture is composed of analog video signals. Accordingly, it is greatly demanded by suppliers of video software such as movies that copy rights be protected, by scrambling the video software broadcasted using the HD system so that viewers cannot record the software. It is also demanded that when video software is recorded for sale on media such as disks and tapes, the video software cannot be copied, by providing a scramble function to a player apparatus.
For viewing a picture which is scrambled as described above and output from an output apparatus such as a broadcast receiver or a player apparatus, a viewer may prepare, for example, a monitor, or the like, which has a descramble function adapted for interpreting the scrambling.
Accordingly, provision of the function of scrambling video signals from a video source in accordance with the HD system to the output apparatus such as the broadcast receiver or the player apparatus is considered.
A plurality of methods of scrambling video signals have been proposed. For example, one of the methods is that the polarity of video signals is switched with predetermined timing in an effective screen interval of the video signals. This method has a problem in that when scrambled video signals are descrambled, it is difficult to completely restore the signals to the state before the signals are scrambled. Therefore, a picture obtained after the video signals are descrambled is inferior to a picture obtained before the video signals are scrambled.
In connection with this method, another method has been proposed in which predetermined processing is used to perform scrambling in, for example, units of fields or units of frames of video signals. One feature of this method is that a possibility of a flicker occurring in a picture obtained after descrambling is increased due to a variation in the gain of an output amplifier in a scramble processing system or an input amplifier in a descramble processing system.
By way of example, since a picture obtained by the HD, system has an image quality higher than that obtained by the SD system, phenomena such as the above-described image-quality deterioration and flicker may cause the resulting image quality to be below an image quality demanded by viewers.
In addition, already known circuit arrangements for scramble processing are, in general, complicated, and therefore increase the manufacturing cost.